A variety of modulation techniques for transmitting digital data on a modulated carrier are known in the field of data communications. For example, one such modulation technique is referred to as phase shift keying (PSK). The phase of the carrier is modulated based on the digital data being transmitted. By detecting the phase of the modulated carrier, it is then possible to recover the digital data from the received carrier.
Binary phase shift keying (BPSK) and quaternary phase shift keying (QPSK) represent two very common forms of PSK modulation. Digital data is encoded as biphase or quadriphase phase changes of a carrier frequency (hereinafter referred to simply as the "carrier"). The recovery of the data requires a carrier-coherent signal for demodulation.
BPSK and QPSK demodulator circuits have been typically constructed with a significant number of analog components. For example, the demodulator circuits usually have included an assortment of analog mixers, summers, oscillators, phase detectors and filters. The number and type of analog components used to construct such a demodulator has been costly and required excessive circuit board space. In addition, significant design effort has been necessary in order to ensure operational compatibility of the various analog components. Digital BPSK and QPSK demodulator circuits have been known to exist. However, these demodulators have been relatively complex and operation intensive.
In view of the foregoing shortcomings associated with conventional PSK demodulators, there is a strong need in the art for a demodulator which utilizes simple digital techniques in lieu of more costly and complex analog and digital designs. Moreover, there is a strong need for such a demodulator that offers a simple construction which can be incorporated easily within an integrated circuit.